SWR pattern of multi-band fan dipole antenna on FM radio band

I had found good reception of FM radio stations using my multi-band fan dipole antenna which works for 40, 30, 20, 15, 10 and 6m amateur radio bands. Set the stimulus range in Nano VNA from 88 MHz to 108 MHz and calibrated using SMA open, short and load connectors. This was the SWR pattern seen on connecting the multi-band fan dipole antenna. There were four dips in SWR across the FM radio band. First dip in SWR was at 89.4 MHZ: 2.177.

Next dip in SWR was at 94.4 MHZ and 1.940.

Third dip in SWR was at 101.000 MHZ and 2.319.

The last dip in SWR was noted at 107.800 MHZ: 1.800. I presume that these dips in SWR would suggest some harmonic resonance of the multi-band fan dipole on the FM radio band. But I had connected only the central conductor of the antenna to the antenna terminal on the FM radio board. Maybe I should try FM DXing after connecting the outer conductor of the PL259 termination of the external antenna to the ground of the FM board as well. Let that be the next experiment in this series!